The invention relates to a pressure medium cylinder, especially a hydraulic input cylinder of the type which can be attached to the chassis of a motor vehicle.
All hydraulically-operated aggregates in motor vehicles are associated, in the layout of the input and output cylinders that operate these aggregates, with certain dimensions that are optimal for the power/displacement ratios. Specifically, it is piston displacement and piston diameter that permit certain operating forces to be transmitted at certain operating displacements.
EP 0 229 350 B1 discloses an operating device having an articulated connection which includes an insertable plastic part, which can be clipped into the pedal and has a ball socket to hold an articulated part. Such a connection greatly simplifies assembly, but is designed for only a single output device, and thus cannot respond to the different requirements for power/displacement ratios in one and the same vehicle type with identical installation conditions for the input-output cylinders.
Depending on the purpose for which they are used, however, vehicles of one and the same type are known to use output devices with very different preloads. Previously, this has required the installation of different types of input-output cylinders. The various sizes of these cylinders and their associated pistons significantly reduce the number of input-output cylinders of one size produced in any single series and accordingly increases the manufacturing costs of the input-output cylinders for one and the same motor vehicle type, even though a sufficient number of such vehicles exist for the rational production of components. The range of power/displacement ratios in one motor vehicle type could generally be covered with two sizes of input-output cylinder. It is therefore proposed to attach the input cylinder to two positions on the pedal, i.e., with different lever lengths, by the articulated part of its tappet.
Such a solution represents a compromise, insofar as the operating displacement of the piston increases along with the lever length. Consistent with the laws of physics regarding levers, the power increases, as desired, as the lever length is reduced. Thus, a design is needed that provides a sufficiently large operating displacement for each of the planned positions. If the operating displacement in the shorter-length position of the articulated part on the pedal is sufficient, then it is only necessary to ensure that the operating displacement in the longer-length position of the articulated part on the pedal is not too great, since this may cause damage to the hydraulic system. In this case, a mechanical stop is needed. The stop can be located on the holding piece with which the input cylinder is arranged on the motor vehicle chassis.
The object of the invention is therefore to provide an input cylinder which, due to the variable connection to the pedal of an articulated part of a tappet for operating a piston of the input cylinder, meets, while using the same attachment parts, different requirements for the power/displacement ratios of the hydraulic operating unit in the motor vehicle.